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3.1. VM Support for Concurrent and Parallel Programming
In Self, the functionality is implemented completely in libraries. The VM
provides only preemptive green threads and the so-called TWAINS_prim primitive.
This provides sufficient VM support to build scheduling, semaphores,
and other abstractions on top.
3.1.2.2. Communicating Threads (ComT)
Similarly to Threads and Locks, the Communicating Threads-based models offer
shared memory and come with the notion of threads as a means of execution.
However, they offer approaches to communicate between threads that
are distinct from approaches that rely on locks for correctness. For instance,
channel-based communication has software engineering tradeoffs different
from the use of locks.
Dis VM The Dis VM [Lucent Technologies Inc and Vita Nuova Limited,
2003] is part of the Inferno OS and hosts the Limbo programming language.
Since the source code does not seem to be available, the analysis relies solely
on the specification and manuals.
Limbo, and consequently the Dis VM are strongly inspired by Hoare’s CSP
(cf. Sec. 2.4.4). However, Limbo and the Dis VM provide the notion of shared
mutable memory between threads and do not follow the notion of isolated
processes as proposed by CSP.
The instruction set of the Dis VM provides operations to mutate shared
memory, spawn threads, and use channel-based communication with sending
and receiving. Since the Dis VM uses a memory-to-memory instruction
set architecture, instead of relying on registers, most operations mutate heap
memory. While threads are available, there are no locking-like primitives or
instructions available. Instead the send, recv, and alt channel operations are
the only instructions in the specification that provide synchronization.
Nevertheless, the Limbo language manual demonstrates how monitors can
be built on top of channels.
Glasgow Haskell Compiler The Glasgow Haskell Compiler (GHC) was one
of the first language implementations to include a software transactional
memory (STM) system in its standard distribution. While Haskell is designed
as a side-effect free language with lazy execution semantics, its monadic-style
can be used in an imperative way, which makes it necessary to coordinate
side-effects when parallel execution is used. To that end, GHC introduced
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